A mechanical lubricant vane pump is generally a volumetric pump which is driven by the engine. The lubricant vane pump is provided with a pump rotor body holding radially slidable vanes rotating inside a shiftable control ring. The slidable vanes, the rotor body, and the control ring wall define a plurality of rotating pump compartments which rotate in a pump chamber. The pump chamber is separated into a charge zone with an inlet opening, a discharge zone with an outlet opening, and an intermediate zone between the charge zone and the discharge zone. The intermediate zone is, seen in a rotating direction, arranged between the charge zone and the discharge zone. The pump compartments rotate from the charge zone, through the intermediate zone, to the discharge zone inside the control ring. The pump comprises a pretensioning element which pushes the control ring to a high pumping volume direction.
The control chamber acts against the pretensioning element when the pressure in the control chamber rises so that, if the rotational speed increases, the control ring is pushed into a low pumping volume direction to keep the outlet pressure constant; if the rotational speed decreases, the control ring is pushed into a high pumping volume direction, so that the lubricant is still pressurized with a more or less constant outlet pressure level more or less independent of the rotational speed of the pump rotor or of the engine.
The lubricant pumped by the lubricant vane pump is incompressible oil with an unavoidable fraction of compressible air. When the rotating pump compartments arrive at the discharge zone, the pressurized lubricant of the pump outlet cavity can flow backwards into the pump cavity so that oscillations of the lubricant volume can occur until the pressure outside and inside this pump compartment is equalized. The lubricant oscillation can lead to high pressure peaks and to hydraulic noise which causes acoustic noise, increased wear, and micro-vibrations of the lubricant vane pump.
Prior art pumps reduce the hydraulic noise of the lubricant vane pumps by pre-compressing the lubricant-air-mixture in the pump compartment passing an intermediate zone between the charge zone and the discharge zone before the pump compartment is connected to the discharge zone. This measure, however, reduces the efficiency of the lubricant vane pump.